Process for forming a patterned thin film structure on a substrate

ABSTRACT

A process for forming a patterned thin film structure on a substrate is disclosed. A pattern is printed with a material, such as a masking coating or an ink, on the substrate, the pattern being such that, in one embodiment, the desired thin film structures will be formed in the areas where the printed material is not present, i.e., a negative image of thin film structure to be formed is printed. In another embodiment, the pattern is printed with a material that is difficult to strip from the substrate, and the desired thin film structures will be formed in the areas where the printed material is present, i.e., a positive image of the thin film structure is printed. The thin film material is deposited on the patterned substrate, and the undesired area is stripped, leaving behind the patterned thin film structures.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of co-pending U.S.application Ser. No. 10/422,557, filed Apr. 23, 2003, the content ofwhich is incorporated herein by reference in its entirety. Saidapplication Ser. No. 10/422,557 claims the benefit of U.S. ProvisionalApplication Ser. No. 60/375,902, filed Apr. 24, 2002, the content ofwhich is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to displays. A process forforming a patterned thin film layer on a substrate is disclosed.

BACKGROUND OF THE INVENTION

A plastic display, such as an electrophoretic display, typicallycomprises two electrodes, at least one of which is patterned, and adisplay medium layer. Biasing voltages typically are applied selectivelyto the electrodes to control the state of the portion(s) of the displaymedium associated with the electrodes being biased. For example, atypical passive matrix electrophoretic display may comprise an array ofelectrophoretic cells arranged in rows and columns and sandwichedbetween a top and bottom electrode layer. The top electrode layer maycomprise, for example, a series of transparent column electrodespositioned over the columns of electrophoretic cells and the bottomelectrode layer may comprise a series of row electrodes positionedbeneath the rows of electrophoretic cells. Several types of passivematrix electrophoretic displays are described in U.S. Provisional PatentApplication Ser. No. 60/322,635 entitled “An Improved ElectrophoreticDisplay with Gating Electrodes,” filed Sep. 12, 2001, U.S. ProvisionalPatent Application Ser. No. 60/313,146 entitled “An ImprovedElectrophoretic Display with Dual mode Switching,” filed on Jul. 17,2001, and U.S. Provisional Patent Application Ser. No. 60/306,312entitled “An Improved Electrophoretic Display with In-Plane Switching,”filed on Aug. 17, 2001, all of which are hereby incorporated byreference for all purposes.

One typical prior art approach to fabricating the patterned electrodelayer(s) for such a plastic display typically involves the use ofphotolithographic techniques and chemical etching. Conductor filmsuseful for plastic display applications may be formed by a process suchas laminating, electroplating, sputtering, vacuum deposition, orcombinations of more than one process for forming a conductor film ontoa plastic substrate. Useful thin film conductors include metalconductors such as, for example, aluminum, copper, zinc, tin,molybdenum, nickel, chromium, silver, gold, iron, indium, thallium,titanium, tantalum, tungsten, rhodium, palladium, platinum and/orcobalt, etc., and metal oxide conductors such as indium tin oxide (ITO)and indium zinc oxide (IZO), as well as alloys or multilayer compositefilms derived from the aforementioned metals and/or metal oxides, e.g.,aluminum zinc oxide, gadolinium indium oxide, tin oxide, orfluorine-doped indium oxide. Further, the thin film structures describedherein may comprise either a single layer thin film or a multilayer thinfilm. ITO films are of particularly interest in many applicationsbecause of their high degree of transmission in the visible lightregion. Useful plastic substrates include epoxy resins, polyimide,polysulfone, polyarylether, polycarbonate (PC), polyethyleneterephthalate (PET), polyethylene terenaphthalate (PEN), poly(cyclicolefin), and their composites. The conductor-on-plastics films aretypically patterned by a photolithographic process which comprisesseveral time consuming and high cost steps including (1) coating theconductor film with photoresist; (2) patterning the photoresist byimage-wise exposing it through a photomask to, for example, ultravioletlight; (3) “developing” the patterned image by removing the photoresistfrom either the exposed or the unexposed areas, depending on the type ofphotoresist used, to uncover the conductor film in areas from which itis to be removed (i.e., areas where no electrode or other conductivestructures is to be located); (4) using a chemical etching process toremove the conductor film from the areas from which the photoresist hasbeen removed; and (5) stripping the remaining photoresist to uncover theelectrodes and/or other patterned conductive structures.

For mass fabrication of a plastic display, such as an electrophoreticdisplay, it may be advantageous to employ a continuous roll-to-rollprocess. However, the photolithographic approach described above is notwell suited to such a roll-to-roll process, as certain of the processingsteps, such as the image-wise exposure, are time consuming and requirecareful registration and alignment of the mask and the moving targetarea. In addition, development and stripping of photoresist andtreatment of waste from the chemical etching process may be timeconsuming and expensive, in addition to potentially posing anenvironmental hazard.

Therefore, there is a need for a process for forming patternedconductive structures on a plastic substrate, for use in a plasticdisplay such as an electrophoretic display, that does not require theuse of photolithography or chemical etching and that is suitable for usein a continuous roll-to-roll process.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings,wherein like reference numerals designate like structural elements, andin which:

FIG. 1 is a flowchart illustrating a process used in one embodiment toform a patterned thin film conductor on a substrate.

FIGS. 2A through 2D illustrate a schematic plan view of a series ofprocessing steps used to form four column electrodes on a substrate.

FIGS. 3A through 3D further illustrate the example shown in FIGS. 2Athrough 2D by providing a schematic front cross-sectional view of theprocessing steps shown in FIGS. 2A through 2D.

FIGS. 4A and 4B illustrate a schematic plan view of an example in whichsegment electrodes for a seven segment display are formed using anembodiment of the process described herein.

FIGS. 5A-1 through 5D-2 illustrate an alternative process used in oneembodiment to form a patterned thin film conductor on a substrate.

FIGS. 6A-1 through 6F-2 illustrate a further alternative to the processshown in FIGS. 1-4.

DETAILED DESCRIPTION

A detailed description of a preferred embodiment of the invention isprovided below. While the invention is described in conjunction withthat preferred embodiment, it should be understood that the invention isnot limited to any one embodiment. On the contrary, the scope of theinvention is limited only by the appended claims and the inventionencompasses numerous alternatives, modifications and equivalents. Forthe purpose of example, numerous specific details are set forth in thefollowing description in order to provide a thorough understanding ofthe present invention. The present invention may be practiced accordingto the claims without some or all of these specific details. For thepurpose of clarity, technical material that is known in the technicalfields related to the invention has not been described in detail so thatthe present invention is not unnecessarily obscured.

A process for forming a patterned thin film structure on a substrate isdisclosed. A pattern is printed with a material, such as a maskingcoating or an ink, on the substrate, the pattern being such that, in oneembodiment, the desired thin film structures will be formed in the areaswhere the printed material is not present, i.e., a negative image of thethin film structure to be formed is printed. In another embodiment, thepattern is printed with a material that is difficult to strip from thesubstrate, and the desired thin film structures will be formed in theareas where the printed material is present, i.e., a positive image ofthe thin film structure is printed. The thin film material is depositedon the patterned substrate, and the undesired area is stripped, leavingbehind the patterned electrode structures.

FIG. 1 is a flowchart illustrating a process used in one embodiment toform a patterned thin film conductor on a substrate. The process beginsin step 102 and proceeds to step 104 in which a negative image of thethin film structures to be formed is printed on the surface of thesubstrate using a masking coating or ink. In one embodiment, the maskingcoating or ink may be stripped using an aqueous solution and/or anothercommon solvent. In step 104, a negative image of the thin filmstructures to be formed is printed in the sense that the masking coatingor ink will cover areas of the substrate where the thin film materialwill not be present upon completion of the process and will not coverareas of the substrate where the thin film material will be present. Inessence, the ink pattern serves as a mask for the subsequent depositionof thin film material, as described more fully below in connection withstep 106.

Any suitable printing techniques, such as flexographic, driographic,electrophotographic, and lithographic printing, may be used to print theink pattern on the substrate. In certain applications, other printingtechniques, such as stamping, screen printing, gravure printing, inkjet, and thermal printing may be suitable, depending on the resolutionrequired. In addition, the masking coating or ink does not need to beoptically contrasted with the substrate, and can be colorless.

In one embodiment, the masking coating or ink comprises a re-dispersibleparticulate. In one embodiment, the masking coating or ink comprises5-80% by weight, preferably 10-60% by weight based on dried weight ofthe masking ink/coating, of a re-dispersible particulate. In oneembodiment, the masking coating or ink comprises a water-soluble orwater-dispersible polymer as a binder. Typical examples of water solublepolymers include, but are not limited to, polyvinyl alcohol,polyvinylpyrrolidone, polyvinylpyridine, polyacrylic acid,polymethacrylic acid, polyacrylamide, polyethyleneglycol,poly(ethylene-co-maleic anhydride), poly (vinylether-co-maleicanhydride), poly(styrene-co-maleic anhydride),poly(butyelene-co-itaconic acid), PEOX, polystyrene sulfonate, cellulosederivatives such as hydroxyethyl cellulose, hydroxypropyl cellulose,methyl cellulose, carboxymethyl cellulose, xanthan gum, gum Arabic,gelatin, lecitin, and their copolymers. In one such embodiment, thewater-dispersible polymer comprises a water- or alkaline-dispersiblewax, polyolefin, or acrylic latexes or dispersions. In one embodiment,the masking coating or ink comprises a solvent-soluble orsolvent-dispersible polymer as a binder. In one embodiment, the maskingcoating or ink comprises a re-dispersible particulate derived fromsilica, CaCO₃, CaSO₄, BaSO₄, Al₂O₃, TiO₂, hollow-spheres,non-film-forming latexes or dispersions, inorganic pigment(s), ororganic pigment(s). In one embodiment, the masking coating or inkcomprises a re-dispersible particulate comprising a polymeric orpolymeric composite particle. In one embodiment, including are-dispersible particulate in the masking coating or ink facilitatessubsequent stripping of the masking coating or ink. In one embodiment,including a re-dispersible particulate in the masking coating or inkfacilitates subsequent stripping of the masking coating or ink byreducing the thickness or integrity of the masking coating or ink layerand/or improving the permeation of a stripping solvent into the maskingcoating or ink layer during stripping.

In step 106, a thin film of material is deposited on the patternedsurface of the substrate. In one embodiment, the thin film material maybe conductive, non-conductive, or semi-conductive. In one embodiment,vapor deposition is used to deposit a thin film of conductive materialon the patterned side of the substrate in step 106. In such anembodiment, aluminum, copper, or any conductive material suitable forbeing deposited as a thin film through vapor deposition or spraying maybe used as the conductive material. In one alternative embodiment, theconductive material is deposited by sputter coating the patterned sideof the substrate with the conductive material. In such an embodiment,indium tin oxide (ITO) or any other conductive material such as gold,silver, copper, iron, nickel, zinc, indium, chromium, aluminum-dopedzinc oxide, gadolinium indium oxide, tin oxide, or fluorine-doped indiumoxide, or any other conductive material suitable for being deposited ina thin film through sputter coating may be used.

In step 108 of the process shown in FIG. 1, the masking coating or inkis stripped from the patterned surface of the substrate on which thethin film material has been deposited in step 106. The stripping of thecoating/ink in step 108 has the effect of stripping away the printedpattern formed in step 104 as well as the portion of the thin filmmaterial deposited in step 106 that was deposited on to the areas of thesubstrate where the coating/ink was present. As a result, the strippingsolvent is able to strip away the coating/ink pattern and the thin filmmaterial formed on the top surface of the coating/ink pattern, eventhough the stripping step is performed after the deposition of the thinfilm in step 106. The process shown in FIG. 1 then ends in step 110.Without limiting the generality of the present disclosure, it isbelieved that in certain embodiments at least part of the maskingcoating/ink printed in step 104 is exposed, or nearly so, to thestripping solvent, despite the masking patterns having been covered withthin film material as a result of the deposition process of step 106. Inone embodiment, low molecular weight additives such as plasticizers,surfactants, and residual monomers or solvents in the maskingcoating/ink may cause defects or micro-porosity in the thin film coatedon the ink, accelerating exposure of the masking coating to the solvent.The present disclosure contemplates that any suitable combination ofcoating/ink, thin film, and stripping process may be used, withoutlimiting the applicability of the present disclosure in any way, andwithout limiting the present disclosure to any particular strippingmechanism or theory. With respect to the process shown in FIG. 1, in anembodiment in which a conductive thin film structure, such as anelectrode or conductive trace, is being formed, the only requirement isthat the combination used be such that, upon stripping, the areas ofthin film formed on the substrate remain present and the areas of thinfilm formed on the strippable masking coating/ink be stripped away, orlargely so, such that the areas where the coating/ink pattern waspresent are not conductive, or sufficiently nearly so for the display tooperate properly.

The process described above does not require the use of photolithographyand selective etching of the thin film layer to define patterned thinfilm structures on a substrate. Instead, the ink pattern is used todefine, prior to the deposition of the thin film material, the shape ofthe thin film structures to be formed. Because a simple solvent, such aswater, aqueous solutions, alcohols, ketones, esters, amides,hydrocarbons, alkylbenzenes, pyrrolidones, sulfones, DMSO, or many othercommon organic solvents or solvent mixture, may be used to strip awaythe ink and the thin film material formed on top of the ink pattern, thepatterned thin film structures may be formed via a roll-to-roll processthat is not as time consuming, not as expensive, and does not generateas much toxic chemical waste as the photolithographic and chemicaletching techniques used in prior art photolithographic processes.

As noted above, one type of display that the above-described process maybe used in connection with is a passive matrix display, such as apassive matrix electrophoretic display. A passive matrix display may,for example, comprise a patterned electrode layer comprising a pluralityof column or row electrodes. FIGS. 2A through 2D illustrate a schematicplan view of a series of processing steps used to form four columnelectrodes on a substrate. FIG. 2A shows a plastic substrate 202. InFIG. 2B an ink pattern comprising lines 204 has been printed on thesubstrate 202. In the example shown in FIG. 2B the lines 204 define onthe substrate 202 areas on which four column electrodes will be formed,as described more fully below, in the areas of substrate 202 that arenot covered by the lines 204.

In FIG. 2C, a thin film layer 206 has been formed on the patternedsurface of the substrate, covering both the portions of the substrate202 that are not covered by the ink lines 204 (shown by dashed lines inFIG. 2C) and the portions that are covered by the ink lines 204. In FIG.2D, the ink pattern has been stripped away, along with the portions ofthe thin film 206 that were deposited on the ink lines 204, exposingcolumn electrodes 208. The respective column electrodes 208 areseparated from each other by the areas of the substrate 202 exposed bythe stripping away of the ink lines 204.

FIGS. 3A through 3D further illustrate the example shown in FIGS. 2Athrough 2D by providing a schematic front cross-sectional view of theprocessing steps shown in FIGS. 2A through 2D. FIG. 3A shows a frontcross-sectional view of the substrate 202. FIG. 3B shows the ink lines204 formed on the substrate 202. As shown in FIG. 3C, the thin filmlayer 206 forms on the portions of the substrate not covered by thelines 204 and on the top and side surfaces of the polymer ink lines 204.Finally, FIG. 3D shows the column electrodes 208 that remain formed onthe substrate 202 subsequent to the stripping of the lines 204, whichhas the effect of stripping away both the ink lines 204 and any thinfilm material 206 formed on top of the ink lines 204.

While FIGS. 2A-2D and 3A-3D illustrate an example in which four columnelectrodes are formed on a plastic substrate, the coating/ink may beprinted in any pattern to define on the substrate thin film structuresof any desired shape or size. FIGS. 4A and 4B illustrate a schematicplan view of an example in which segment electrodes for a seven segmentdisplay are formed using an embodiment of the process described herein.FIG. 4A shows display electrode layer 400 comprising a polymer inkpattern 402 defining on a plastic substrate seven segment electrodeareas 404 a-404 g in which the ink pattern 402 is not present such thatthe underlying substrate is exposed. FIG. 4B shows the same displayelectrode layer 400 subsequent to the steps of deposition of the thinfilm and stripping of the ink pattern. As shown in FIG. 4B, thestripping away of the ink exposes a background area 406 of the substrateon which no thin film structure is present. In addition, segmentelectrodes 408 a-408 g have been formed and remain in the segmentelectrode areas 404A-404G defined as described above in connection withFIG. 4A.

As is apparent from the above discussion, thin film structures of anyshape or size may be formed simply by defining through use of theprinted pattern areas on the substrate on which thin film structures areto be formed. The structures may include electrode structures such asthose described above and/or conductive traces or any other thin filmstructure desired.

The processes described herein may be used in one embodiment to form atop or bottom electrode layer to be disposed adjacent to anelectrophoretic display media layer. In one embodiment, theelectrophoretic display media comprises a layer of sealed microcups,each comprising a quantity of electrophoretic dispersion. In oneembodiment, a protective overcoat such as an antiglare protectivecoating comprising particulate filler may be applied onto the sealedmicrocups or the top (viewing side) electrode layer to further improvethe optical or physicomechanical properties of the finished panel.

In one embodiment, conductive thin film structures are formed on boththe top and bottom surfaces of the substrate, using the processdescribed herein first to form thin film structures on one side of thesubstrate and then to form thin film structures on the opposite side ofthe substrate using the same series of steps described above for formingthin film structures on one side of the substrate. In one embodiment,conductive thin film structures on the top surface of the substrate maybe connected electrically to conductive surfaces formed on the bottomsurface of the substrate by forming via holes and completing anelectrical connection through the via hole from a conductive structureon the top surface of the substrate to a conductive structure on thebottom surface of the substrate, as described in U.S. patent applicationSer. No. 10/422,413, which is incorporated herein by reference.

In one embodiment of the process illustrated in FIGS. 1-4, thecoating/ink used to pattern the substrate comprises Sun ChemicalAquabond AP blue ink and/or Sunester red ink (Sun Chemical, Northlake,Ill.) and the substrate comprises 5 mil thick Melinex 453 polyester(DuPont Teijin, Hopewell, Va.). The ink may be applied through a stencilusing a hand proofer with a #360 anilox roller. The ink may be driedwith a heat gun. The thin film material is deposited by loading thepatterned substrate into a DC-magnetron sputtering system to deposit ITOfilm up to about 100 nm thickness. The patterned substrate may be plasmatreated prior to deposition of the thin film. The ink pattern and thinfilm formed thereon is stripped by spraying the patterned substrate onwhich the thin film has been formed with acetone (Histological grade,Fisher Scientific) for 1 to 2 minutes at room temperature. The aboveprocessing steps result in the thin film (i.e., ITO) formed in the inkpattern being removed along with the ink, leaving an area on thesubstrate where no ITO coating is present such that no measurableconductivity in present in such areas where the ITO has been removed.

In one embodiment of the processes illustrated in FIGS. 1-4, Film IIIWarm Red ink (Environmental Inks and Coatings, Los Angeles, Calif.) isapplied using a hand proofer to define a pattern or mask on a substratecomprising 5 mil thick Melinex ST505 polyester (DuPont Teijin, Hopewell,Va.). The thin film is deposited by loading the patterned substrate intoa DC-magnetron sputtering system to deposit ITO film up to about 100 nmthickness. The ink is washed from the ITO coated patterned substrate byspraying with acetone (Histological grade, Fisher Scientific) for 30 to60 sec. The ITO formed on the ink is removed along with the ink, leavingan area where there is no ITO coating where the ink pattern was printed.

In one embodiment of the processes illustrated in FIGS. 1-4, the inkpattern is printed on 5 mil thick, 4507 Polyester (Transilwrap, FranklinPark, Ill.) using GP-217 Process Magenta ink (Ink Systems Inc.,Commerce, Calif.) on an offset press. The inked polyester is loaded in avacuum system for aluminum evaporation at the film thickness of 120 nm.The aluminum coated polyester is immersed in hot (T=about 80° C.) methylethyl ketone (Certified grade, Fisher Scientific, MEK) for 15 seconds,and then wiped gently with a cotton swab soaked in MEK. This processstrips the inked area from the polyester, along with the aluminum on topof the ink. The stripping results in a negative image from the ink,i.e., there is no aluminum coating in the areas where the ink patternwas printed, with the remaining areas (i.e., where the ink pattern wasnot present) being coated with aluminum.

In one embodiment of the processes illustrated in FIGS. 1-4, an inkpattern is made on a roll of 5 mil thick, 12″ wide Melinex 453 polyester(Plastics Suppliers, Fullerton Calif.) using Film III Warm Red ink(Environmental Inks and Coatings, Los Angeles, Calif.) on a Mark Andy4200 flexographic press. The patterned polyester is loaded into aDC-magnetron sputtering system to deposit ITO film for about 100 nm.Prior to the deposition, the ink coated sheets may be plasma treated.The ITO coated polyester is then immersed in a jar of hot (T=about 80°C.) MEK and cleaned ultrasonically using a Fisher Scientific FS220Hultrasonic cleaner for 2 minutes. As a result of the ultrasonic cleaningstep, the ink is stripped from the polyester, along with the ITO formedon top of the ink.

In one embodiment in which conductive structures are formed on both thetop and bottom surfaces of the substrate, the processes illustrated inFIGS. 1-4 may comprise printing on both sides of a roll of Melinex 561polyester (10″ wide, 4 mil thick, DuPont Teijin Films, Wilmington, Del.)using Film III Warm Red Ink (Environmental Inks and Coatings, Morganton,N.C.) on a Mark Andy 4200 flexographic press. In one embodiment, thefirst side is printed with a first pattern A at one printing station,the web is run through a turn bar that flips the web, and the other sideof the substrate is aligned and printed with a second pattern B at thenext plate station during the same printing run. In one embodiment, thefirst pattern A comprises a negative image defining ink free areas inwhich segment electrodes are to be formed, and the second pattern Bcomprises a negative image defining ink free areas in which conductivelines are to be formed. The patterns are aligned such that each ink freesegment electrode area in pattern A is aligned with the end of one inkfree conductive line in pattern B, such as may be desirable to allow foran electrical connection to be made between a segment electrode of sideA and a conductive line of side B through a conductive via structurethrough the substrate. In one embodiment, about 40′ of the polyesterprinted on both sides is sputtered on both sides with 2500 angstroms ofaluminum. A 5″×5″ piece of the aluminum coated polyester is developed byimmersing it in a crystallizing dish containing methyl ethyl ketone, andputting the dish into a Fisher #FS220H ultrasonicator (FisherScientific, Pittsburg, Pa.) filled an inch deep with water for 2minutes. This yields a polyester electrode with one side having aluminumonly in the segment pattern of the ink free areas of A, and the oppositeside having the electrode pattern of the ink free lines in B.

The ability to strip away the masking coating/ink lines after depositionof the thin film using a simple stripping process that is notdestructive of the thin film formed in the areas where the coating/inkpattern is not present (such as but not limited to the solvent andphysical peeling processes described above) facilitates a continuousfabrication process, such as a roll to roll fabrication process, becauseno time consuming batch processes such as image-wise exposure anddevelopment of photoresist, etching away portions of a thin film layernot covered by photoresist, or using solvents requiring special handlingor conditions to remove a photoresist layer after etching, are required.By saving time and using less expensive materials, the process describedherein is much less costly than other processes typically used to formon a polymer substrate the types of structures described herein.

FIGS. 5A-1 through 5D-2 illustrate an alternative process used in oneembodiment to form a patterned thin film conductor on a substrate. Thealternative process shown in FIGS. 5A-1 through 5D-2 employs a“positive” printed image in the sense that the coating/ink is printed inthe pattern of the thin film structure(s) to be formed, instead of beingused as described above in connection with FIGS. 1-4 to define areaswhere the thin film structure(s) is/are not to be formed. The processillustrated in FIGS. 5A-1 through 5D-2 is similar to that shown in FIGS.1-4 in that the process shown in FIGS. 5A-1 through 5D-2 employsprinting techniques to define the thin film structure(s) to be formed.The process shown in FIGS. 5A-1 through 5D-2 differs from the processshown in FIGS. 1-4, however, in that the printed pattern is not strippedoff the substrate, as described more fully below.

As shown in FIGS. 5A-1 and 5A-2, the thin film structures are formed ona substrate 502. The substrate 502 may be any of the substrate materialsdescribed above for use in the process illustrated by FIGS. 1-4. In oneembodiment, the substrate comprises 5 mil thick, 4507 Polyester(available from Transilwrap, Franklin Park, Ill.). FIGS. 5B-1 and 5B-2show pattern lines 504 and 506 printed on the substrate 502. In oneembodiment, the pattern lines 504 and 506 are printed on the substrate502 using GP20011 UV Process Magenta ink (Ink Systems Inc., Commerce,Calif.) on an offset press. Any ink or other printable material may beused that has the characteristic that the subsequently deposited thinfilm adheres to the printed material more strongly than it adheres tothe substrate, as explained more fully below.

FIGS. 5C-1 and 5C-2 show a thin film layer 508 being formed on thepatterned surface of the substrate, covering both the printed pattern(lines 504 and 506) and the areas of the substrate 502 not covered bythe printed pattern. In one embodiment, the thin film 508 is formed byloading the patterned substrate into a vacuum system for aluminumevaporation at a film thickness of 120 nm.

FIGS. 5D-1 and 5D-2 show the remaining structures after the portions ofthe thin film 508 formed on the substrate 502 have been removed by astripping process. Thin film structures 510 and 512 remain formed onprinted lines 504 and 506, respectively. In one embodiment, a solvent isused to remove the portions of the thin film formed directly on thesubstrate, but not the portions of the thin film formed over the printedmaterial, leaving thin film structures in the same pattern as theprinted material. In one embodiment, not shown in FIGS. 5D-1 and 5D-2,some or all of the thin film formed on the side surfaces of the printedmaterial remains adhered to the side surfaces of the printed materialafter the stripping process. In one embodiment, not all of the thin filmformed directly on the substrate is removed by the stripping process,but the thin film formed directly on the substrate is removedsufficiently to cause there to be no measurable conductivity in theareas of the substrate where the printed material was not printed.

The alternative process shown in FIGS. 5A-1 through 5D-2 requires thatthe adhesion of the thin film layer to the substrate be low, theadhesion of the thin film layer to the printed material be high, theadhesion of the printed material to the substrate be high, and that thesolvent be such that it removes the portions of the thin film layer thatare formed directly on the substrate but not those portions of the thinfilm layer formed on the printed material.

In another alternative process, a substrate having a poor affinitytoward the thin film may be used. In one such embodiment, a surfacetreatment or primer coating such as a UV curable polymer layer, havinggood adhesion to both the substrate and the thin film is used to replacethe masking coating/ink in steps 104 and 106 of the process shown inFIG. 1. In this case, the thin film on the uncoated areas will beremoved in the stripping process to reveal the electrode pattern ortrace on the top of the surface treatment or primer coating. Thisalternative process is similar to that shown in FIGS. 5A-1 through 5D-2,with the primer coating comprising the printed material, such as patternlines 504 and 506.

FIGS. 6A-1 through 6F-2 illustrate a further alternative to the processshown in FIGS. 1-4. FIGS. 6A-1 and 6A-2 show a substrate 602. In FIGS.6B-1 and 6B-2, pattern lines 604 and 606 have been printed onto thesubstrate 602 using a printable first material. In one embodiment, asshown in FIGS. 6C-1 and 6C-2, the printed substrate is then over-coatedwith a second material that is not soluble in at least one solvent inwhich the first printable material is soluble, such that said at leastone solvent could be used to strip the first printable material withoutalso stripping the second material. In one embodiment, the printablefirst material is hydrophobic (ie., water repelling) and solvent solubleand has a low surface tension. In one embodiment, the second material iswater-based and is repelled by the first material, such that theovercoat adheres only to those portions of the substrate not covered bythe first material, forming areas 608, 610, and 612 comprising thesecond (water-based) material. In one alternative embodiment, the secondmaterial is not repelled by the first material and the second materialmay partially or fully overcoat the pattern lines 604 and 606 shown inFIGS. 6C-1 and 6C-2. In one such embodiment, in the regions in which thesecond material overcoats the first material, the second material may beless thick than in regions in which the second material is applieddirectly to the substrate (i.e., regions on the substrate in which thefirst material is not printed). In one embodiment, the first material isstripped using a suitable solvent that does not also strip away thesecond material, leaving the structure shown in FIGS. 6D-1 and 6D-2, inwhich the structures 604 and 606 comprising the first material have beenstripped away, leaving the structures 608, 610, and 612 comprising thesecond material on the substrate 602. In one embodiment in which thesecond material may partially or fully overcoat the printed firstmaterial, portions of the second material so formed on the firstmaterial are stripped away along with the portions of the first materialon which they are formed, leaving the portions of the second materialapplied directly to the substrate (i.e., in regions where the firstmaterial was not present), as shown in FIGS. 6D-1 and 6D-2. In oneembodiment, the solvent used to strip away the first printable material(and, if applicable, portions of the second material formed thereon)comprises an aqueous solution or water. In one embodiment, the solventused to strip away the first printable material comprises a non-aqueoussolvent or solution. Next, as shown in FIGS. 6E-1 and 6E-2, a thin film614 is formed both on the structures 608, 610, and 612 and on theportions of the substrate 602 not covered by the second material, usingone of the thin film materials described above. In one embodiment, thethin film is formed by sputtering, vapor deposition, spraying, or someother suitable technique. Finally, FIGS. 6F-1 and 6F-2 show the thinfilm structures 616 and 618 that remain after the second material hasbeen stripped away with an appropriate solvent, or another appropriatechemical or mechanical stripping process. In one embodiment, the solventused to strip away the first material is an aqueous basic solution andthe solvent used to strip away the second material is an aqueous acidicsolution, an aqueous neutral solution, or water. In one embodiment, thesolvent used to strip away the first material is an aqueous acidicsolution and the solvent used to strip away the second material is anaqueous basic solution, an aqueous neutral solution, or water. In oneembodiment, the solvent used to strip away the first material is anaqueous neutral solution or water and the solvent used to strip away thesecond material is an aqueous acidic solution or an aqueous basicsolution.

Under the process shown in FIGS. 6A-1 through 6F-2, the printed patternof the first material comprises a positive image of the thin filmstructures to be formed. Once the first material has been stripped away,as described above, the remaining second material comprises a negativeimage of the thin film structures to be formed. In a sense, the firstmaterial may be considered a mask that may be used to define areashaving very small dimensions, such as very fine lines, in which the thinfilm structures will not be present. While it may be difficult withpractically useful printing techniques, such as flexographic, to printsuch narrow lines in the first instance, for example because of physicallimitations, spreading of the ink after printing, etc., such techniquesmay be used readily to print less fine lines or less small areas withonly small gaps separating the lines or areas. A second material such asdescribed above may then be used to fill in the narrow spaces betweenthe areas covered by the first material, which first material may thenbe stripped away using an appropriate solvent, leaving behind very finelines or other shapes comprising the second material, which very finelines or shapes it may not have been practical to print in the firstinstance. These lines may then be used, as described above, as anegative image for the formation of adjacent thin film structuresseparated by very narrow gaps, for example.

In one embodiment, a physical stripping process such as peeling is usedto reveal the thin film structures. For example, an adhesive tape havingan appropriate cohesion strength and adhesion strength to ITO islaminated onto an ITO/PET film pre-printed with a masking coating/ink. Asubsequent peeling will remove the ITO either on the area printed withmasking ink or on the area without the ink depending on the cohesionstrength of the ink and the adhesion strengths at the ink-PET andITO-PET interfaces. This stripping technique may be used with any of theprocesses described above.

In one embodiment, the process of FIGS. 6A-1 through 6F-2 comprisesprinting a positive image of desired thin film thin film structures on aroll of Melinex 582 polyester (4 mil thick, 14″ wide, Dupont TeijinFilms, Wilmington, Del.) using Film III Warm Red Ink (Environmental Inksand Coatings, Morganton, N.C.) on a Mark Andy 4200 flexographic press.The printed portion of the polyester roll is then coated with a solutionconsisting of 16 parts of aqueous 10% polyvinyl pyrrolidinone (PVP-90,ISP Technologies, Inc., Wayne, N.J.), 0.40 parts Sunsperse Violet (SunChemical, Cincinnati, Ohio), and 16 parts water using a #6 Meyer bar,and dried 1.5 minutes in an oven at 80° C. The film is then placed in acrystallizing dish containing ethyl acetate. A 10″×10″×12.5″ultrasonication bath (BLACKSTONE-NEY, PROT-0512H EP ultrasonic bathdriven by a 12T MultiSonik™ generator) is filled with about 4″ of waterand the dish containing the film is floated in the water andultrasonicated at 104 KHz for 5 minutes. The film is then removed fromthe dish and dried 1.5 minutes in an oven at 80° C. At the completion ofthe drying step, the film has lines of PVP coating that define anegative image of the originally printed positive image. The patternedpolyester is next sputter coated with ITO using a CHA Mark 50 rollcoater to deposit a 1250 angstroms thick ITO film. The ITO coatedpatterned polyester is then ultrasonicated for 3 minutes in a beakercontaining water placed in a Fisher #FS220H ultrasonicator (FisherScientific, Pittsburg, Pa.). The film is then rinsed with de-ionizedwater and dried by blowing the water off with a stream of air. Theresulting film has ITO structures in the shape of the originally printedpositive image.

In one embodiment, the process shown in FIGS. 6A-1 through 6F-2comprises sputter deposition of ITO film on a PET substrate having ahydrophilic coating, e.g., Melnix 582, and printed using warm red ink(Environmental Ink). In one embodiment, this combination of materialsallows the ITO to be stripped from undesired areas ultrasonically usinga water based stripper.

In one embodiment, the water based stripper for ITO stripping could be asurfactant solution such as JEM-126 (sodium tripolyphosphate, sodiumsilicate, nonyl phenol ethoxylate, ethylene glycol monbutyl ether andsodium hydroxide), detergent formulation 409, hydroproxide, anddeveloper Shipley 453, etc.

In one embodiment, the ITO stripping rate depends on the solventconcentration, solvent temperature, and the position of the substratefilm relative to the ultrasound transducer.

In one embodiment, prior to the ITO sputter deposition, the ink printedPET surface is pre-treated with an appropriate plasma. In oneembodiment, such plasma pretreatment minimizes the generation ofmicro-cracks on the patterned ITO structures during the ITO strippingprocess. In addition, such plasma pre-treatment may in one embodimentprevent ITO residue from being generated on the printed ink area as aresult of removal of part of the printed ink pattern due to high-energyplasma, which may generate ITO residue on the printed ink area duringthe stripping process.

In order to eliminate the optical impact of minor ink residue appearingon the stripped ITO surface, in one embodiment a colorless ink printedon the PET surface is preferred.

The additional examples listed below (identified as Embodiments Athrough F to facilitate comparison) further illustrate the benefits, interms of the patterning of thin film and the related manufacturing andhandling processes, e.g., of including in the masking coating/ink are-dispersible particulate as described herein, such as in the processesdescribed above in connection with FIGS. 1 through 4B.

In an Embodiment A, the following masking layer composition was used foraluminum (Al) metal thin film patterning: 5.5 grams Celvol 203S (PVAfrom Celanese, Dallas, Tex., LMW, 87% hydrolysis), 5.5 grams PVP K-30(from ISP Corp., Wayne, N.J.), and 0.1 grams of Xanthan Gum (fromAllchem, Inc., Dalton, Ga.) were dissolved slowly at room temperatureinto 39.2 grams of de-ionized water. To the masking composition, 0.23grams of Silwet L-7608 (from OSi Specialties, Middlebury, Conn.), wasadded. The resultant solution was used as the masking coating/ink forprinting a pattern on a substrate for metallization, e.g., as describedherein.

In an Embodiment B, the following masking layer composition was used foraluminum (Al) metal thin film patterning: 3.0 grams of 20% dispersedsilica (Sylojet 703C, from Grace Davison, Columbia, Md.) was dilutedwith 36.2 grams of de-ionized water. To this solution, 5.2 grams Celvol203S, 5.2 grams PVP K-30 and 0.1 grams of Xanthan Gum were added slowlyat room temperature then mixed at high shear rate. Finally, 0.23 gramsof Silwet L-7608 was added. The resultant solution was used as themasking coating/ink for printing a pattern on a substrate formetallization, e.g., as described herein.

In Embodiments C-F, the same procedure and binders of Embodiment B wereused, except that the weight percent of Silica in the dried films werechanged to 10% in Embodiment C, 30% in Embodiment D, 60% in EmbodimentE, and 80% in Embodiment F.

For purposes of comparison, all of the masking solutions in theabove-described Embodiments A-F were screen printed on to a 2 milMelinex 453 PET film (ICI, UK) through a 330 mesh stencil to form anegative masking pattern. The roll-up properties of the printed filmwere evaluated by the blocking resistance at ambient and 50° C./80% RHconditions. The printed PET film was uniformly coated with an Al layerof 50 to 60 nm thickness by vapor deposition. Positive Al pattern wasdeveloped in water by selectively stripping off the Al layer on themasking layer to generate positive Al pattern on the area that was notprinted with the masking layer. The stripability or strippingselectivity is determined by the sharpness and shininess of theresultant Al image. The results are listed in Table 1 below (with theembodiment to which the data in each row applies indicated by the letterin the first column):

TABLE 1 Film Silica Film Blocking Binder (wt Blocking after agingPVA/PVP % in Screen at in Stripability K-30 dried Printing ambient 50°C./80% of Al by (1:1) film) quality condition RH Water A 97  0% GoodBlocking Blocking Good severely B 92  5% Good Excellent Good Good C 8710% Good Excellent Excellent Excellent D 67 30% Good Excellent ExcellentExcellent E 37 60% Good Excellent Excellent Excellent F 17 80% FairExcellent Excellent Fair-Good

It can be seen from Table 1 that the addition of the particulate silicafrom 5 wt % to 80 wt % based on the dried masking film improvessignificantly both blocking resistance of the masking layer and thestripability of the Al layer on the masking layer. The presence of theparticulate dispersion in the masking layer also resulted in highlyshiny Al lines with fine line width and excellent integrity.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. It should be noted that there are many alternative waysof implementing both the process and apparatus of the present invention.Accordingly, the present embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein, but may be modified within the scope andequivalents of the appended claims.

1. A process for forming a thin film structure on a substrate,comprising: printing on the substrate with a first material a patternthat defines a positive image of the thin film structure such that thefirst material is printed in the area where the thin film structure isto be formed, the first material being strippable using a first solvent;overcoating the printed surface of the substrate with a second materialthat is not strippable using the first solvent; stripping the firstmaterial away using the first solvent in a process that strips away thefirst material and the second material formed on the first materialwithout stripping away the second material formed directly on thesubstrate, such that the second material remains coated on the substratewhere the first material was not present, thereby defining a negativeimage of the thin film structure such that the second material is notpresent in the area where the thin film structure is to be formed;depositing a thin film material on the patterned surface of thesubstrate; and stripping the second material and the thin film materialdeposited on the second material to form the thin film structure.
 2. Theprocess for forming a thin film structure on a substrate as recited inclaim 1, wherein the first material repels the second material that thesecond material fills in the areas of the substrate where the firstmaterial has not been printed without coating the areas where the firstmaterial is present.
 3. The process for forming a thin film structure ona substrate as recited in claim 1, wherein the first solvent is anaqueous solution or water.
 4. The process for forming a thin filmstructure on a substrate as recited in claim 1, wherein the firstsolvent is a non-aqueous solvent or solution.
 5. The process for forminga thin film structure on a substrate as recited in claim 1, wherein thefirst solvent is an aqueous basic solution, and the step of strippingthe second material comprises using a second solvent comprising anaqueous acidic solution, an aqueous neutral solution, or water.
 6. Theprocess for forming a thin film structure on a substrate as recited inclaim 1, wherein the first solvent is an aqueous acidic solution and thestep of stripping the second material comprises using a second solventcomprising an aqueous basic solution, an aqueous neutral solution, orwater.
 7. The process for forming a thin film structure on a substrateas recited in claim 1, wherein the first solvent is an aqueous neutralsolution or water and the step of stripping the second materialcomprises using a second solvent comprising an aqueous acidic solutionor an aqueous basic solution.